Within the total IBA1+ population (macrophages + microglia), we saw that only 20% of the total IBA1+ population was comprised of microglia at two weeks post implantation (Fig. 9G).

Additionally, at chronic time points (four, eight and sixteen weeks), we observed that less than 40% of the total IBA1+ population was comprised of microglia (Fig. 9G).

On the other hand, no significant differences were observed in microglia populations over time (Fig. 9G, Table 4). Together, our results suggest a predominant role of infiltrating macrophages surrounding implanted microelectrodes over time.

IBA1 = marker for ionized calcium binding adapter molecule, to label the total population of microglia/ macrophages (both resting and activated)

CD68 = activated microglia / macrophage.

Hard to discriminate microglia and infiltrating macrophages.

Interestingly, fluctuations in GFAP+ immunoreactivity correlated well with neuronal density and CFP+ immunoreactivty, suggesting a possible role of astrocytes in facilitating trafficking of blood-derived cells.

Contrary to what has been suggested by many intracortical microelectrode studies, a consistent connection was not found between activated microglia/macrophages and neuron density in our chimera models